1. Field of the Invention
The present invention relates generally to transcutaneous energy transfer in implantable medical devices and, more particularly, to an adjustable transcutaneous energy transfer system.
2. Related Art
Medical devices having one or more implantable components, generally referred to as implantable medical devices, have provided a wide range of therapeutic benefits to patients over recent decades. Implantable medical devices often include one or more instruments, apparatus, sensors, processors, controllers or other functional components that are permanently or temporarily implanted in a patient. The implanted components are used to, for example, diagnosis, monitor, or treat a disease or injury, or to modify the patient's anatomy or a physiological process. Many of these implantable components receive energy (i.e. power and/or data) from external components that are part of, or operate in conjunction with, the implantable component. Implantable hearing prostheses that treat the hearing loss of a prosthesis recipient are one particular type of implantable medical devices that are widely used today.
Hearing loss, which may be due to many different causes, is generally of two types, conductive and sensorineural. In some cases, a person suffers from hearing loss of both types. Conductive hearing loss occurs when the normal mechanical pathways for sound to reach the cochlea, and thus the sensory hair cells therein, are impeded, for example, by damage to the ossicles. Individuals who suffer from conductive hearing loss typically have some form of residual hearing because the hair cells in the cochlea are undamaged. As a result, individuals suffering from conductive hearing loss typically receive an implantable hearing prosthesis that generates mechanical motion of the cochlea fluid. Some such hearing prosthesis, such as acoustic hearing aids, middle ear implants, etc., include one or more components implanted in the recipient, and are referred to herein as implantable hearing prosthesis.
In many people who are profoundly deaf, however, the reason for their deafness is sensorineural hearing loss. Sensorineural hearing loss occurs when there is damage to the inner ear, or to the nerve pathways from the inner ear to the brain. As such, those suffering from some forms of sensorineural hearing loss are thus unable to derive suitable benefit from hearing prostheses that generate mechanical motion of the cochlea fluid. As a result, implantable hearing prostheses that deliver electrical stimulation to nerve cells of the recipient's auditory system have been developed to provide the sensations of hearing to persons whom do not derive adequate benefit from conventional hearing aids. Such electrically-stimulating hearing prostheses deliver electrical stimulation to nerve cells of the recipient's auditory system thereby providing the recipient with a hearing percept.
As used herein, the recipient's auditory system includes all sensory system components used to perceive a sound signal, such as hearing sensation receptors, neural pathways, including the auditory nerve and spiral ganglion, and parts of the brain used to sense sounds. Electrically-stimulating hearing prostheses include, for example, auditory brain stimulators and cochlear prostheses (commonly referred to as cochlear prosthetic devices, cochlear implants, cochlear devices, and the like; simply “cochlear implants” herein.)
Oftentimes sensorineural hearing loss is due to the absence or destruction of the cochlear hair cells which transduce acoustic signals into nerve impulses. It is for this purpose that cochlear implants have been developed. Cochlear implants provide a recipient with a hearing percept by delivering electrical stimulation signals directly to the auditory nerve cells, thereby bypassing absent or defective hair cells that normally transduce acoustic vibrations into neural activity. Such devices generally use an electrode array implanted in the cochlea so that the electrodes may differentially activate auditory neurons that normally encode differential pitches of sound. Auditory brain stimulators are used to treat a smaller number of recipients with bilateral degeneration of the auditory nerve. For such recipients, the auditory brain stimulator provides stimulation of the cochlear nucleus in the brainstem.